Wireless devices such as terminals are also known as e.g. User Equipments (UEs), mobile terminals, stations (STAs), wireless terminals, communication devices and/or mobile stations. Terminals are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or tablets with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB, micro eNodeB or pico base station, based on transmission power, functional capabilities and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Machine Type Communication (MTC) is about providing connectivity for devices, e.g. MTC devices such as wireless devices, which communicate without human interaction. It is predicted to increase the number of connections exponentially more than the increase of human subscriptions and the number of fixed connections. This is sometimes referred to as ‘the networked society’. Because of the different nature, the requirements for MTC are also different from those of human oriented smart phone traffic. For example, MTC devices need to have low cost, which is achieved by low UE complexity and reduced capabilities, e.g. one receiving antenna, a narrow device bandwidth that is smaller than the system bandwidth, etc. The power consumption should further be low in order to prolong battery life such that interactive battery charging is not required. By interactive battery charging is meant battery charging requiring human interaction to for example connect a cord to a power supply. Preferably, the battery should last, without requiring recharging, throughout the life span of the device. To be able to reach devices in challenging location, such as basements, it is desirable to enhance coverage in comparison to normal systems.
In 3GPP, Rel-13 MTC, work is ongoing to support coverage enhancements of up to 15 dB. This is achieved by time repetition in a Transmission Time Interval (TTI) bundling manner, similar to that introduced for Voice over IP (VoIP) in Rel-8. In Rel-8, TTI bundling is limited to the uplink shared data channel and fixed to 4 repetitions. For Rel-13 MTC devices requiring coverage enhancements, the number of repetitions may be configured per coverage area, e.g. cell, or per wireless device, e.g. UE. Link simulations show that the number of required repetitions may be over 100 to achieve the targeted 15 dB gain for some channels.
In Rel-12 a lower complexity UE category 0 (Cat-0) was introduced to support lower manufacturing costs for MTC devices. In Rel-13 further complexity reductions are being introduced where the largest change is a reduced device bandwidth from e.g. 100 to 6 Physical Resource Blocks (PRBs) or from 20 MHz to 1.4 MHz. This means that some legacy channels like the Physical Downlink Control CHannel (PDCCH), which spans over the entire system bandwidth, cannot be received. The working assumption for these low complexity UEs is to replace PDCCH with an updated version of Enhanced Physical Downlink Control CHannel (E-PDCCH) transmitted only within 6 PRBs (referred to as MTC PDCCH (M-PDCCH). The lower complexity of the devices means that a small number of repetitions might be needed also for these devices in normal coverage. That is, the repetitions are needed to counteract the losses from using only one receiving antenna (Rel-12), loss of frequency diversity (Rel-13), etc. Further, due to the extended transmission time resulting from the repetitions, the working assumption is to have cross-subframe scheduling. That is, a transmission is first scheduled by repetitions on E-PDCCH and then the repetitions of the actual data transmission are carried out first after the final transmission of the E-PDCCH.
The document “SIB for Rel-13 low complexity and coverage enhanced UEs” (3GPP draft; R2-153711, Mobile Competence Centre; 650 Route des Lucioles; F-06921 Sophia-Antipolis, vol. RAN WG2, no. Beijing, P.R. China; 20150824-30150828 23 Aug. 2015 (2015 Aug. 23)) discusses system information design for Rel-13 low-complexity and coverage enhanced UEs (Rel-13 LC/CE UEs), focusing on SIB1x/SI scheduling. It is disclosed that the SIB1x contains detailed scheduling information such as time, frequency, and Modulation and Coding Scheme (MCS)/Transport Block Size (TBS), by means of which subsequent SIBs can be acquired without reading PDCCH.
US 2009/0262693 A1 discloses a method and an apparatus for allocating sub-frames in a system information transmission window, allocating transmission sub-frames consecutively at the beginning of the system information transmission window, allocating non-transmission sub-frames at end of the system information transmission window, and transmitting the system information transmission window.